Lattice with smaller momentum compaction factor for PEP-II high energy ring

Abstract

At present, the PEP-II bunch length and vertical beta function /spl beta//sub y/*, at the Interaction Point (IP) are about of the same size. To increase luminosity, it is planned to gradually reduce /spl beta//sub y/*. For the maximum effect, bunch length has to be also reduced along with /spl beta//sub y/* to minimize luminosity loss caused by the hourglass effect at IP. One of the methods to achieve a smaller bunch length is to reduce momentum compaction factor. This paper discusses a lattice option for the High Energy Ring,where the nominal 60/spl deg/ cells in four arcs are replaced by 90/spl deg/ cells to reduce momentum compaction factor by 30% and bunch length by 16%. The increased focusing in 90/spl deg/ cells results in 40% stronger,arc quadrupoles and 150% stronger arc sextupoles due to reduced dispersion and larger chromaticity. Tracking simulations predict that dynamic aperture for this lattice will be /spl ges/ 10 times the rms size of a fully coupled beam for a horizontal emittance of 30 nm and,/spl beta//sub y/* = 1 cm. The lattice modification and results of simulations are presented.